Do you sound like your parents? Or like the people you grow up with? What about the way you dress, or the music you listen to, or the way you spend your free time?

Behavioral trait? Stable property of a person that can be measured by standardized psychological tests Intelligence tests (IQ) Personality tests (profile) Life outcomes = psychiatric diagnoses, marriage stability, brushes with the law

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable The Second Law: The effect of being raised in the same family is smaller than the effect of the genes The Third Law: A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable Heritability Proportion of variance in a trait that correlates with genetic differences Measured in several ways: correlation between identical twins separated at birth (share the same genes but grew in diff environment) = any correlation is an effect of their genes Correlation between identical twins (share all their genes/most of their environment) reared together with fraternal twins (share half of their genes/most of their environment) reared together Biological siblings (half of their genes/most of their environment) vs adoptive siblings (none of their genes/most of their environment)

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable Heritability Identical twins reared apart are highly similar Identical twins reared together are more similar than fraternal twins reared together Biological siblings are far more similar than adoptive siblings Substantial heritability values = bet.25 to.75 Conventional summary: About half of the variation in intelligence, personality and life outcomes is heritable – a correlate or an indirect product of the genes

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable Heritability Issues in precision values Whether measurement error (random noise) is included in the total variance Whether all the effects of the genes are being estimated or only additive effects (ones that exert the same influence vice other genes) Variation in the sample: samples with homogenous environment give large heritability estimates, those with varied give smaller ones Heritability of intelligence increases over life span (as high as.8 in life)

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable “ all traits are heritable” is a bit of an exaggeration but not by much Content of home or culture, not heritable: language you speak, religion you worship, political party you belong Traits that reflect underlying talents and temperament are heritable: how proficient in language, how religious, how liberal/conservative General intelligence is heritable 5 major ways in which personality can vary (OCEAN) Openness to experience Conscientiousness Extroversion-introversion Neuroticism

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable Specific traits are heritable: alcohol/nicotine dependence, television watching hours, likelihood of divorcing As long as the heritability of talents and tastes is not zero, none of us has a way of knowing whether a trait has been influenced by our genes, our childhood experiences, both or neither The 1 st law implies that any study that measures something in parents and something in their biological children and then draws some conclusions about the effects of parenting is worthless, because the correlations may simply reflect the shared genes (aggressive parents may breed aggressive children, talkative parents talkative children)

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable Critics: Children separated at birth deliberately placed in similar adoptive families They have contact with each other Parents expect identical twins to be more alike and so treat them alike Shared prenatal experience, not their shared genes that make them more alike Differences in home environments do not produce differences in grown children’s intelligence and personality

Law Of Behavioral Genetics The First Law: All human behavioral traits are heritable 3 built-in limitations: Can help explain what makes people different but not what they have in common (universal human nature).5 intelligence does not imply that half of the person’s intelligence is inherited but implies only that half of the variation among people is inherited Address variation in within the group examined and not between groups of people Can’t show why White’s differ from Black’s; middle-class from lower class Can show only that traits can correlate with genes, not directly caused by them Height and looks are heritable but their effects are not [not all attractive women are vain and entitled]

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes We are shaped both by our genes and our environment (family upbringing)…???? The shared environment is what impinges on us and our siblings alike: parents, home life, neighborhood Non-shared environment is everything else: anything that impinges on one sibling but nor another (parental favoritism); unique experience like being infected by a virus; experiences that does not necessarily happen to our siblings Effect of shared environment can be measured in twin studies by subtracting the heritability value from the correlation between the identical twins

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes We are shaped both by our genes and our environment (family upbringing)…???? The shared environment is what impinges on us and our siblings alike: parents, home life, neighborhood Non-shared environment is everything else: anything that impinges on one sibling but nor another (parental favoritism); unique experience like being infected by a virus; experiences that does not necessarily happen to our siblings Effect of shared environment can be measured in twin studies by subtracting the heritability value from the correlation between the identical twins

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes Identical twins (share genes and environment) minus (sum of the effect of genes, the shared environment and the unique environment) Adoptive: heritability estimate – shared environment estimate Findings: Effects of shared environment are small (less than 10 percent of the variance), often not statistically significant, often not replicated in other studies, and often a big fat zero They are negligible, particularly in adulthood {IQ is affected by the shared environment in childhood, but over the years the effects peters out to nothing]

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes Where do these conclusions come from: Adult siblings are equally similar whether they grew up together or apart Adoptive siblings are no more similar than 2 people plucked off the street at random Identical twins are no more similar than one would expect form the effects of their shared genes Whatever experiences siblings share by growing up in the same home makes little or no difference in kinds of people they turn out to be

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes Impt proviso: Differences among homes don’t matter within the samples of homes netted by these studies which tend to be more middle- class than the population as a whole But differences between those samples and other kinds of homes would matter Can’t say anything about differences between cultures – what makes a child a middle-class American to a Tibetan monk or member of an urban street gang If a sample comes from a restricted range of homes, it may underestimate effects of homes across a wider range

Law Of Behavioral Genetics The Second Law: The effect of being raised in the same family is smaller than the effect of the genes But…the 2 nd law is not trivial The ‘middle-class’ [which includes most adoptive parent] can embrace a wide range of lifestyles, with very different home environments and child-rearing philosophies Behavioral geneticists have found that their samples of parents in fact span a full range of personality types

Law Of Behavioral Genetics The Third Law: A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families/ Follows directly from the 1 st law, assuming that heritabilities are less than one and the 2 nd law Identical twins reared together are far from identical in their intellects and personalities There must be causes that are neither genetic nor common to the family that make identical twins different and more generally what make people what they are

Law Of Behavioral Genetics Handy summary of the 3 laws: Genes 50 percent [40-50], Shared environment 0 [0-10], unique environment 50 percent [50] Identical twins are 50 percent similar whether they grow up together or apart So what do we really know about long-term effects f parenting? Natural variation among parents and the raw material of behavioral genetics offers way of finding out…

Law Of Behavioral Genetics If anything that parents do affects their children in any systematic way, then children growing up with the same parents will turn out more similar than children growing up with different parent… but they don’t Second law implies that sibling s reared together end up no more similar than siblings separated at birth…their similarities could be accounted for by their shared genes

Do you sound like your parents? Or like the people you grow up with? What about the way you dress, or the music you listen to, or the way you spend your free time?

Socialization-acquiring the norms and skills necessary to function in society – takes place in the peer group (Group socialization theory of Harris) It’s not all in the genes but what is not in the genes is not from the parents either